The present invention relates to the use of melamine formaldehyde-type polymers to control and/or inhibit stickies deposition in secondary fiber pulping and papermaking processes. More particularly, this invention relates to inhibiting the deposition of stickles or tackles on machinery used in secondary fiber pulping and papermaking processes and to the removal of stickles from machinery used in secondary fiber pulping and papermaking processes. Improved paper products resulting from use of the instant method are also included within the scope of this invention.
Stickies and tackles continue to be a problem in secondary fiber pulp and paper mills. It is believed that the problems caused by the build up of stickies and tackles on pulp and papermaking machinery and in the final paper cost the pulp and paper industry many millions of dollars per year in lost production. The terms "stickles" and "tackies" as used herein, are interchangeable terms that primarily include synthetic contraries found in secondary fiber. For example, stickles and tackles include, but are not limited to, ink residuals, tars, latexes, adhesives and heat melt contaminants found in secondary fiber and in systems where paper produced in a mill is used as broke. As such, stickies and tackies are distinct from pitch, which is defined as any resin-based deposit of widely varying constituency originating in the extractive fraction of wood. The extractive fraction of wood is a complex mixture of substances which are soluble in water, alcohol, benzene, ether, and/or acetone. The extractive fraction, which generally makes up from about 3% to 10% of the weight of wood, contains such components as low molecular weight carbohydrates, terpenes, aromatic and aliphatic acids, alcohols, tannins, color substances, proteins, lignins, alkaloids, and soluble lignins. The constituents of pitch are naturally occurring, as opposed to the synthetic compounds that comprise stickies. While pitch and stickies cause similar problems in papermaking operations, they are distinct both in terms of their origin and their composition.
Stickles and tackies are a major problem in secondary fiber pulp and papermaking operations because they (1) agglomerate and also occlude other matter to form visible "dirt" in the final paper, (2) plate out and collect on machinery used in pulping and papermaking process such as screens, filters refining equipment, pulp washers, and paper machines, and (3) reduce pulp brightness and brightness stability. The composition and amount of stickies deposited on pulping and papermaking machinery and in the final paper varies with the type of secondary fiber used in the pulping operation. As used herein, the term "secondary fiber" includes any paper fiber used for a second time in the production of a paper end-product.
Sources of secondary fiber include, but are not limited to, tissue, fine paper, boxboard, linerboard, foodboard and newsprint. Each of these sources generally contains unique impurities, such as inks, colors, fillers, strength resins and/or coatings, which means that the stickies composition and concentration can vary widely from one secondary fiber to another.
The presence of calcium carbonate in the pulping process generally exacerbates the problem of stickies deposition on pulp and papermaking machinery. Crystallized calcium carbonate can provide nucleation sites for precipitated metal soaps thereby producing hydrophobic particles which coalesce with other particles to form a stickies deposit.
There have been many attempts over the years to eliminate stickies problems by adding control agents to secondary fiber pulping and/or papermaking processes. While more thorough deinking and pulp washing operations may help to reduce stickies problems, the most common methods of treatment involve the addition of dispersants or adsorbent fillers to the furnish. For example, treatments may involve the use of zirconium compounds, alum, talc, anionic stickies-control agents such as polynaphthalene sulfonates or modified lignosulfonates, cationic control agents such as polyquaternary ammonium polymers, methylcellulose derivatives and nonionic surfactants. None of these treatments are believed to be particularly effective for stickles control.
Examples of the use of poly quaternary ammonium polymers as pitch control agents can be found in U.S. Pat. No. 3,582,461. The '461 patent discloses the use of water soluble dicyandiamide-formaldehyde condensates to prevent pitch deposition on machinery used in pulping and papermaking processes. By contrast, the instant invention utilizes water insoluble acid colloids for stickles control.
Examples of attempts to control pitch with other types of compounds or processes are found in U.S. Pat. Nos. 3,812,055; 3,895,164; 3,896,046; 3,992,249; 4,313,790.
Zirconium chemicals have also been used to control pitch and stickies. See, for example, U.S. Pat. No. 4,950,361.
The instant melamine formaldehyde-type polymers are widely used in water treatment, particularly in the treatment of paint spray booths. See, for example, U.S. Pat. Nos. 4,656,059, 4,629,572, 4,935,149 and 5,068,279.
Copending and commonly assigned application U.S. Ser. No. 07/878,637, now U.S. Pat. No. 5,286,347, relates to the use of melamine-formaldehyde-type polymers as pitch control agents.
The use of melamine formaldehyde-type polymers to control stickies deposition in papermaking is not known or suggested in the art.
As indicated above, the present invention relates primarily to the inhibition and/or control of stickies in secondary fiber papermaking operations. For purposes of this invention, pitch is defined as the material comprising naturally occurring resinous materials and gums liberated during the screening, heating and refining processes that occur during papermaking. Stickies, on the other hand, are defined as synthetic impurities which are present in secondary fiber paper furnishes. More particularly, stickies are defined as adherent deposits caused by organic materials used in paper and board coating and converting operations which are typically introduced into paper machine furnishes with recycled fibers. The word "stickies" is derived from the fact that the resultant deposits stick to wires, felts, and other parts of paper machine. Stickies also trap inorganic components found in papermaking furnishes. Stickies are a diverse mixture of synthetic materials ranging from hot-melt and pressure-sensitive adhesives to binders and coatings for inks or wet strength resins. Polymeric examples include, for example, polyethylenes, polybutadiene-styrenes, polyvinylacetates and polyacrylates.